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<h3 class="section" id="Interacting-with-the-GCC-Garbage-Collector"><span>24.4 Interacting with the GCC Garbage Collector<a class="copiable-link" href="#Interacting-with-the-GCC-Garbage-Collector"> &para;</a></span></h3>

<p>Some plugins may want to be informed when GGC (the GCC Garbage
Collector) is running. They can register callbacks for the
<code class="code">PLUGIN_GGC_START</code> and <code class="code">PLUGIN_GGC_END</code> events (for which
the callback is called with a null <code class="code">gcc_data</code>) to be notified of
the start or end of the GCC garbage collection.
</p>
<p>Some plugins may need to have GGC mark additional data. This can be
done by registering a callback (called with a null <code class="code">gcc_data</code>)
for the <code class="code">PLUGIN_GGC_MARKING</code> event. Such callbacks can call the
<code class="code">ggc_set_mark</code> routine, preferably through the <code class="code">ggc_mark</code> macro
(and conversely, these routines should usually not be used in plugins
outside of the <code class="code">PLUGIN_GGC_MARKING</code> event).  Plugins that wish to hold
weak references to gc data may also use this event to drop weak references when
the object is about to be collected.  The <code class="code">ggc_marked_p</code> function can be
used to tell if an object is marked, or is about to  be collected.  The
<code class="code">gt_clear_cache</code> overloads which some types define may also be of use in
managing weak references.
</p>
<p>Some plugins may need to add extra GGC root tables, e.g. to handle their own
<code class="code">GTY</code>-ed data. This can be done with the <code class="code">PLUGIN_REGISTER_GGC_ROOTS</code>
pseudo-event with a null callback and the extra root table (of type <code class="code">struct
ggc_root_tab*</code>) as <code class="code">user_data</code>.  Running the
 <code class="code">gengtype -p <var class="var">source-dir</var> <var class="var">file-list</var> <var class="var">plugin*.c</var> ...</code>
utility generates these extra root tables.
</p>
<p>You should understand the details of memory management inside GCC
before using <code class="code">PLUGIN_GGC_MARKING</code> or <code class="code">PLUGIN_REGISTER_GGC_ROOTS</code>.
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